1. Field of the Invention
The present invention relates generally to the field of high voltage vacuum switches and circuit interrupting devices and more particularly to a toroidal vacuum interrupter for modular multi-break switchgear.
2. Discussion of the Prior Art
Single vacuum interrupters utilized in high power switchgear have generally been limited to the voltage range below 46 kV. In modern vacuum switchgear, multiple vacuum contact breaks have been employed to provide higher voltage ratings.
A number of vacuum prior art arrangements are directed to provide a vacuum interrupter with two or more contacts within the same envelope as illustrated in U.S. Pat. Nos. 3,250,880; 3,405,245; 4,107,496; 4,246,458 and 6,476,338 B2. The first three cited patents present devices in which two moving contact structures must be moved in opposite directs to achieve two series contact breaks, necessitating a complex and costly operating mechanism. The latter two patents represent devices that rely on the transfer of the electric arc to one or more sets of auxiliary contacts as the moving contact is drawn past them. This can result in longer arcing times as the moving contact is drawn through its stroke to establish the multiple breaks as well as severe erosion along the edges of the contacts at the arc transfer points.
A more common practice for creating switchgear with two or more contact breaks in series is to simply mount the required number of single break vacuum interrupters in series as shown by U.S. Pat. Nos. 2,859,309; 3,792,213; 3,813,506; 3,839,612; 4,027,123; 4,972,055; 6,242,708; 6,498,315 B1; 7,239,492 B2. This practice requires the use of complex and costly interconnecting mechanisms for the series interrupter modules and results in a bulky switchgear unit.
Another prior art interrupter utilizes multiple contact systems where one set of contacts drives another as illustrated in U.S. Pat. No. 2,863,026. In this case, the operating spring for the driven contact is mounted inside the interrupter and is subject to annealing during the brazing together of the interrupter. While work hardening will result in the return of some of the spring force characteristics, its final force characteristics will be uncontrolled. Additionally, no means is provided to precisely position the driven contact, adjust out the tolerance accumulation between the multiple parts or to balance the voltage between the two contact gaps.
U.S. Pat. No. 3,283,101 and Patent application publication no. US 2007/0262054 A1 disclose a double break vacuum interrupter, which is operated by a single moving contact rod. The first cited patent shows an extremely complex method of assuring that the contacts make and break at the same time and does not indicate the use of capacitance to balance the voltages between the two contact gaps. With the cited patent application, there is no indication of how tolerance accumulation of the components and contact wear are accounted for to assure that both contact breaks can continue to make over the life of the device. In addition, the fact that the contact structures are mounted in a parallel configuration results in a bulky vacuum module.
Patent application publication no.: US 2010/0108643 A1 also discloses a double break vacuum interrupter, which is operated by a single contact rod. This device contains an internally mounted bellows like spring, which would become annealed during the interrupter brazing cycle and would greatly affect its force characteristics. The spring would regain some of its spring force with work hardening; however, its final force characteristics would be uncontrolled. When the contacts close, the contact rod drives one moving contact into the second moving contact and then the second contact into the stationary contact which provides for making only one set of contacts instead of two, which can result in a longer pre-strike and possible welding. In addition, there is a further possibility of contact welding as the contact rod only drives one contact open, with the internal spring returning the other contact to the open position.
While the aforementioned prior art arrangements may be suitable for their intended use in accordance with their respective defined applications, as discussed hereinbefore, it would be desirable to provide a system of vacuum switch or interrupter modules that may be connected in series and driven by a single contact rod to allow for the fabrication of various forms of high voltage switchgear at different voltage ratings